The present invention is within the immunology field and particularly the field of neutralizing antibodies directed against antigens of virus pathogens.
More specifically, the invention relates to a monoclonal antibody directed against the VP1 protein of JC virus (JCV).
JC virus (JCV) is a human polyomavirus of the Polyomaviridae family and the agent responsible for an extremely serious, often lethal, demyelinating disease designated as progressive multifocal leukoencephalopathy (PML). JC virus has an envelope-less icosahedral capsid that encloses a circular double-stranded DNA genome. The major capsid component is the viral protein VP1. Structural studies done on virions revealed that the polyomavirus capsid is made of 72 pentamers formed by VP1 monomers linked through the C terminal end. VP1 binds to the receptors on target cells and thereby starts infection.
JC virus infects over 85% of adult humans. After the primary infection, JC virus stays quiescent in the kidneys and lymphoid organs. In healthy individuals this virus can replicate in kidney tubule cells and is excreted in the urine, without causing any disease. However, in cases of serious immuno-depression, in subjects who received an organ transplant, in oncologic patients, in patients treated with the novel monoclonal antibody-based immunomodulatory therapies, or in people suffering from AIDS, JC virus can spread to the central nervous system and cause progressive multifocal leukoencephalopathy (PML). In the pre-cART (combination antiretroviral therapy) era, PML incidence in HIV patients ranged from 0.3% to 8%, but the extensive use of antiretroviral treatments determined a significant decrease thereof. HIV infection is the immunodeficiency cause still most frequently associated to PML, with approximately 80% of cases, followed by hematologic tumors (approximately 8%), solid tumors (approximately 3%), organ transplants, and autoimmune diseases treated with immunomodulators.
However, in the last ten years increasing numbers of PML cases non-HIV/AIDS-correlated were reported. Many of these new cases occur in individuals subjected to immunotherapies with recently available drugs. By Feb. 29, 2012, 212 cases of PML connected with natalizumab treatment have been documented, with respect to 99571 patients suffering from multiple sclerosis treated throughout the world with this drug. PML has also been correlated to other immunomodulatory therapies, including efalizumab, mycophenolate mofetil, and rituximab.
For treatment of PML, several therapeutic strategies have been attempted, which were directed against different viral replication cycle phases, such as for example entry into the target cell and replication of the genome. However, none of them gave significant beneficial effects. On the basis of a connection between PML and serious immuno-depression conditions, immunological approaches were also attempted. For instance, patients suffering from PML with a more favorable prognosis were shown to be characterized by a stronger JCV-specific cell-mediated and humoral response. The potential importance of a specific anti-JCV response, particularly against VP1, was confirmed by the strong neutralizing activity of animal (rabbit) sera immunized with the JCV VP1 protein (Goldmann C et al. Journal of Virology, May 1999, pages 4465-4469).
An alternative therapy based on anti-JCV antibodies could thus be applied to treatment of patients suffering from PML. Particularly, in view of the key role of VP1 protein in the early phases of JCV infection, the best candidates could be antibodies against the JCV VP1 protein.
Such a need has now been met by the present inventors who, for the first time, succeeded in obtaining fully human monoclonal antibodies directed towards the JCV VP1 protein and having a neutralizing activity against the virus, which makes them suitable for use in the therapeutic treatment of PML.
These results are to be considered new and surprising in the light of the state of the art, as no human anti-JCV VP1 monoclonal antibody has been so far described, least of all a human anti-JCV VP1 neutralizing monoclonal antibody.
Goldmann C et al. supra, described hyper-immune sera with rabbit anti-VP1 antibodies evoked by virus-like particles having neutralizing properties against JCV.
The Japanese patent application JP9067397A mentioned a method for obtaining a neutralizing anti-JCV antibody, which comprises immunizing rats with a synthetic peptide corresponding to a portion of the VP1 protein, collecting the immune sera from the rats, and separating a fraction of gamma-globulins. In this patent the selection of a monoclonal antibody was not mentioned, least of all one derived from man.
The anti-JCV VP1 monoclonal antibody designated as ab34756, marketed by Abcam®, United Kingdom, is a murine antibody used for detecting the virus through ELISA and Western Blot, clearly not suitable for therapeutic applications, least of all in the human being.
Therefore, none of the anti-JCV antibodies of the prior art would potentially be suitable to be used in therapeutic or prophylactic applications for JCV infections or diseases correlated with the same in human patients.
It is also to be pointed out that, before the testing done by the present inventors, the person of skill in the art reasonably would not have expected to obtain fully human anti-JCV monoclonal antibodies capable of neutralizing JC virus, as no scientific publication was available wherein the presence of neutralizing anti-JCV antibodies had been assessed accurately in the human humoral response. By way of example, the paper by G. Bloomgren et al. N Engl J Med 2012; 366: 1870-80 is mentioned, wherein the authors propose a risk stratification for PML in patients suffering from multiple sclerosis. For the risk stratification, the authors propose three risk factors, that is the presence or absence of anti-JCV antibodies, the previous use of immunosuppressants, and the length of treatment with natalizumab, but they do not propose or mention in any way the assessment of the presence of neutralizing antibodies in the human humoral response. On the other hand, the prior art points out the technical problems connected with the detection of the humoral anti-JCV response in the human being, for instance in Raphael P. Viscidi and Barbara Clayman, Advances in experimental medicine and biology 2006; 577( ): 73-84 and in Wendy A. Knowles, Advances in experimental medicine and biology 2006; 577( ): 19-45.